Department of General Practice and Primary Care, Guy's, King's and St Thomas's School of Medicine, London SE1 7EH

EDITOR—One of the central issues in the debate about informed consent in randomised controlled trials1 has been the ethics of withholding the fact of randomisation from participants—for example, in the trials of support after stroke2 and of management of sore throat.3 Psychologists recognise that it is sometimes necessary to withhold full information from participants, to minimise bias. Our professional code of conduct (http://www.bps.org.uk/charter/codofcon.htm) states that in these situations we must “provide … full information …